Voice-frequency signaling



sMW /KY W m MWWMWW hm W m J VOICE FfiE UENQY SIGNALING A. B. CLARK ET AL Original Filed Nov. 17, 1921 t Ia'20cyde 50mm Patented Dec.l16, 1 924."

UNITED STATES P TENT orrlcs.

ALVA; B. CLARK, or saooxmrn, AND DANFORTH K. GANNET'I AND HARRY NYQoIs'r,

- OF ELMHURST, NE'W YORK, ASSIGNORS TO AMERICAN TELEPHONE AND TELE- GRAPH'COMPANY. i. CORPORATION OF NEW YORK.

VOICEFREQUENCY SIGNALING.

- 'Appliatioh m November 17, 1921, Serial No. 515,881. Renewed r m 30, 1924.

Bexit known that we, Anvil ll. CLARK,

"DANroiz'rIr K. GANNE'IT, and HARRY- NY- and Q. 1eens and State of New York, re-

spectively, have invented. ('Glttllll IlDPlOVO- ments in Voi(e-Frequency Signaling, 'of

- which the following is a specification. I

p This im entlon relates toisignalmg and more particularly to methods or and means Tor-transmitting and receiying ringing signals in telephone transmission systems.-

In present day' telephone and telegraph practice it is customary to'prow ide' a trans mission system with a plural ty of channels, each of which serves to transmit current in-p --dependently" of the others.' Interference between the-variouschannels is prevented by. employingfor each channel dnl" erent-:fre-- quencies or hands of fretpienciesan'd appa- .'-.;rat'us selectivelyresponsive thereto. The

frequency-range is thus divided into a number of ,levels,'and a separate transmission channel is' provided for each; frequency.

level, Two of the channels used in teleph0ne.prnctice are the voice channel and'the ringing channel, the frequency level of the "latter being'genera lly below that of the 30. former... For example, the ringing currents might have a frequency in the neighborhood M135. cycles, whereas the components of'thc' '-voice currents would have frequencies-vary" ingfromjabout 300 to 2000 cycles. v This arrangement necessitatcs'at repeater and similar: installations th'g: .proi ision'='of separate repeating or relayingapparatusi apparatus. I In Fig.1 arcshoivntwo' stations, A and f I provide arrangements whereby a false operation of the signaling-apparatus by the actual voice currents may be prevented. To

accomplish this purpose the currents of voice frequency, when utilized for signaling purposes, are generated and transmitted out over the system in an intermittent or p'eriodic manner as a'set of impulses-aha predetel-mined rate, this rate being determined, if desired, by thefrequency of the signaling current at the switchboard. The receiving apparatus 1s then'so designed as to-respond to interruptions'of'the voiceffre'quency .cu r-- rent'at this predetermined rate only and to be unresponsive to other .currentswithin the voice frequency range which do "not have th s predetermined intermittent characteristlc; Other'featl'iresmnd purposes of the invention will'appear more fully' from the detailed description hereinafter'given. '-'lh'e'1nvent1on is"1llustrated-in the accompanying drawing, n'the Figure-l of which while'in the Fig. ilis-shoirnin detail" the cir cult arrangement of a portion of the ringing is shown "a schematic arrangement thereof.

B, interconnected by the lineL. The trans-.

mission line-L may include such apparatus as composite sets, phantom coils or repeaters illustrated schematically as the arrange- 1nents'52 and 53.. Bridged across the transmission line at the stationA by conductors such'asl and 2, 'or-other-suitable switching arrangements; are the i'ieircuits L and .L,. The circuit L assoc ated with a .20 cycle 7 ';-generatingapparatusWand s20 cycle're 1 40 frequenciesv are. ineflieientl at the ringing frev tionapiiopose's to do away with this duplica- -:ringin'g-; andvoice currents; foi--;the--ree enwiring-apparatuses] The circuit L is asso- 'thatco ls and amplifiers, efiicient at vo ce; clatedwlth' a voice frequency receiving apquency andjvice versa.'- :The"p'resent invenapparatusitx WVhenthe operator at circuit tion of apparatus, by raising the ringing vparatus 5 and a voice frequency-generating transmits lowfrequency signaling current into thelme, such as 20cycle current, a part vchafr'ir'iel to, the same frequencylevel as that 4 ofith'e voice channel, sothat the same apparatus may be efficiently employed for the transmission of currents of both.

'- It-is' a'further feature of theinvention to ofthiai current will be transmitted over circuit li to the 20 cycle receiving apparatus 4 which, upon responding thereto, will op erate the relay'8. The relay 8 will connect circuit L to'the voic e frequency generating.

- current-- within'the' voice frequency range.

The voice frequency signals coming in from a station such as B will botransmitted over circuit L to the voice frequency receiving apparatus 5, which, upon responding thereto, will operate the relay-7. The relay 7 will'connect the circuit L, to the 20 cycle generating apparatus 3 whereby the low frequency signaling currents suitable for operating the apparatus at the switchboard of station A wil e transmitted thereto. Similar arrangements to those already described with res ect to station A will be provided at station 1; associated with conductors 1 and 2 and the circuits L, and L Considerible advantages are secured by bridging the ringer arrangements of'this invention across the line'L by the conductors 1' and 2 and 1.

and 2 instead of connecting it in series with the circuit as has heretofore been the practise as relay and jack contacts are eliminated from the telephone circuit and the wiring is greatly simplified.

In Fig. 2 are shown in detail the arrangements of the low frequency and the voice frequency receivers and generators associated with the transmission line at each station. Associated with line L, is the filtering device F, which readily allows the transmission ofthelow frequency signaling currents, such as 20 cycle currents,- transmitted from the switchboard. This filtering device is so designed that it has a very high inlpedance to voice frequencies and therefore prevents the 20 cycle relays and circuits about-to be described from causing an appreciable loss of energy to the speech currents or to the voice frequency signaling currents. The filter also serves to prevent voice frequenc harmonics in the 20 cycle current from thus to L and the voice frequency receiving circuit, and lockin the latter in operated position. The line is associated with the windin s of'a polar relay 14, which is operated y the 20 cycle current transmitted from the switchboard, The 20 cycle current from the switchboard will be transmitted over the contacts of relay 9 and thence over conductors 13, 12'and 10 through the windings of the polar relay 14 and also through the winding of relay 11. This will operate the-relay 11 as wellas the'relay 14. The p operation of relay 11 "closes the' following circuit: from battery, conductor 29, contact and. armature of relay 11, conductor 30, winding of relay 28, conductors 31 and 20 to ground. The closing of this circuit will operate relay 28which will disconnect 'conductor 26' from conductor 54 and connect it to conductor 18 thereby disconnecting the voice .frequency receiving apparatusiwhich will be described later, from the line, and

eing transmitted to L, andconnecting the voice frequency generating, ap YtratllS to the line.

, e voice'frequencygenerator consists ofan oscillatin circuit controlled by the polar 1 r'ela 14; 1%16 polar relay'14 in response 70 to t e 20 cycle signaling cnrrentmlternately charges and disc urges the condenser 16 in the oscillating circuit. 20- times a second; When the armature of relay 14 rests on the right-hand contact, the oscillating circuitin- Z eludes the condenser 55, which ischarged to the otential of battery 56, conductor 21, the rig t-hand contact and armature of re-.. lay 14, condenser 16, inductance 15, conductor 18, make contactand armature of relay 28, conductor 26, winding of traumaformer 19 conductors 17, 24 and 20 to ground. when the armature off r-clay 14- rests on the left-hand contact, -t}i cire it is the same as aboveexcept thalfxondensei 55 and conductors 21, 2t) and 24ers no longer in circuit, the circuit being estabg lished directly from condenser 16 to con-f 'ductor 17 'thru the left-hand contact of relay 14. The inductance 15, together with c'a' pacity 16, tunes the oscillating circuitto be resonant at 800 cycles. The alternate (am-3; ing and discharging of the condenser 20 times a second in the oscillating circuit creates a damped train 'of 800 e do oscillations for each charge and foreac discharge. These oscillations are transmitted from the oscillating circuit through the transformer 19 to circuit L and thence. out over the line. The relation of the design of transformer 19 to the line impedance connected to line L, and to the impedance of the oscillating cir cuit just described, is such as to cause the line resistance to provide the proper dhmp ing coetiicient to the oscillations toobtain it the optimum results. i

The voicefrequency receiving arrangements are connected to line L, through transformer 19 and include a series resonant circuit 32 tuned to approximately 800 cycles. 5" The series resonantcircuit 32'is of low impedanc'e as it is impracticable to construct such a circuit to have i himpedance.v To" prevent this low i'm'pc ancc circuit drom causing too great a. loss in the telephone 1,! circuit the transformer 19, through which-2 it is connected to the line is constructed to operate asan ine uality ratio coiland'to .1 step up the impe ance in the proper ro- 5.4. ortion. In 'practicethe series resonant 'i'rcult may-not betuned to the exact carrier, frequency of the incoming signal, such'as."

800 cycles, but is tuned slightly lower. This series resonant circuit .is an amplifier and detector 34 of the wellknown vacuum bulb type. Associated. with theoutput trans- .former'ofthe'tube is abridgedcondenser 35' .whi6fi" tunes it to be resonant at d0 cycles, which is theirequency of occilr'rb'hceof the ,trains of 800 cycleoscillations transmitted over the line'Lffrom the -generating circuit at the distant station} This arrangement results'in maximum -sensitivity to. the ring-' fing signal and lowersensitivity to inter- 1ference The 40 cycle current thus produced by the detecting action of the vacuum bulb .1 former .36 to a polar relay 37v and serves to operate this 'relay at the same frequency of --'40"cycles. This vibrating operation of the 1 j polar relay the.succeeding'neutral-relay 40 in the fol- ';lowing manner: Each time the armature of a the olar -relay37 strikes, the lower contact 3 oon ensues 'isjcharged to the potential of A -'-"batt ery 56 througlithe circuit. from conout') over; conductor 45 and 44 the lower ,relay icontact and the relay armature. The -'other,terminal"offcondenser 38 is grounded --'through conductors,39, A3 and When' 11 ";tlfieparmatiirefiof; the polar relay 37 strikes t e'jjup gn1ru relay 40; and-conductors 4:1, 42, 4'3 and 2O to groundi 'The -sensitivity of lrelay 40 is'such that when the polar relay operates :withaspeed (ii-approximately cycles'the discharges of condenser 38 produce enough =currentto' operate saidrelay. Operation of 1 the polar relay at an appreciably lower speed "than atl'fcycles; however, does notresult in 40'. suflicient current in relay 40 to cause its 3 operation. This prevents false operation of relay 40 frominterference of, such a nature- "as to cause ,a low frequency operation of the E *polar relay. 1 4a When" relay 40 operates," its contacts open up the circuit which otherwise exists I through the windin of relay 46. This circuit is as follows om ground and battery a 5G, coil-22, conductors, 23 and 45, winding 6010f rela 4'6, resistances '50, contact of rela 40' an Upon opening of the contact ofrelay 40, Y howeverythe current does not immediatelycease flowing in the winding of relay 46 but a5 'continues to flow into condenser 57 until the latter is'charged to the potential of the I A 1 battery 56. l his causes relay 4:6 to release with 'a certain' time lag with respect to the --operation of relay 40, which lag is deter- .L'60 "minedjby, the Qsensitivit of relay 46 and by the-time"constant of t e c'ondenser 57 and f -"the-res'istance 5(l which is in series with relay 1146; This time lag serves as an additional 1 check-to prevent any false operation of the 37 causes sustained operation of.

. denserfwhich-is'maintained at the po-. ,tentialbfr attery.. 56, as hasbeen pointed,

er {contact condenser 38 discharges.-

conductors 42 a'nd'43 to groun signaling means which might occur should. the actual voice currents which are not mtended for signaling purposesscrve to actuate the relay 37 and the relay 40.-

suchactuat on' of these relays would only bed a temporary nature, the relay 40' would As any be restored to normal before the'rela'y 16' could operate. under. these conditions, dlS- charging condenser '57- and' re-establishing the currentthrough tlieflatte r relay; When the relay 46 is released,the following circuit is closed: ,from ground; conductorsglii and 4:2, armature an ground, thereby operating relay .9. "This will-connect'to'the lineL the conductors ,481

At the close'of the ringing signal, polar relay 37 stops vibrating and'rclay'40is re-' leased, '-returning to'its normalunoperated- I contact of relay46, con- 1'34 is transmitted by the tuned output transductor 47,.Winding of mayors battery; and

position. Relay .46, however, operates with termined by the time constant nf-the con a time lag which is shorter .than the lag at the beginning of the ring, and which is defeature has been found valuable in prevent ing interference with. the ringing signal by disturbingcurrents'; "fl- 1 1 While th low frequency'ringiiigjcurrent mately' 2;) cycles, and the voicefiequency mately 800 cycles, it is pointed out that-this has been referred to as-currentiofapproiri invention -.is not limited to thesefrequencies but' that other suitable frequencies may be utilized. Furthermore, While thc-farrange 1' ments of the invention have been disclosed in certain specific forms which are deemed desirable, it is understood that'they "are capable of embodiment in many varied forms without departin from the spirit of the invention as define "in the appended claims.

\Vhatisclaimed is:' f 1. A transn'iiss'ion line intercom .cting-two stations, means at one of said stations for generating current within thevoice frequency range, means for applying said current to saidfline in a periodically interrupted mannca' according 170 21 predetermined fre ice and widely quency, and receiving means at said other station exclusively responsive. to currents periodically interrupter according to said predetermined frequency. t

'2. A transmission line interconnecting two stations, a low frequcncy'signaling source at one station, signaling apparatus at said station comprising a vibrating relay controlled by the fiequency of said signaling current from said station, an oscillating circuit con trolled by said relay and tuned to :1 frequency within thevoice range whereby there will be generated trains of oscillations of a periodicity controlled by the frequency of vibration of said relay, and means for con- 5 pling said circuit to said line.

3. A transmission line interconnecting two stations, :1 low frequency signaling source 'at 1 one station, signaling apparatus at said .sta-

tion comprising a vibrating relay controlled by said low frequency signaling current. from said station, an oscillatingcircult icontrolled by said relayand tuned to a frequency within the voice range whereby there will be generated trains of-oscil-lations of a periodicity controlled by the frequency of vibration of said relay, and means for coupling said circuit to said line, and signaling apparatus at the other station comprising means exclusively responsive to trains of oscillations of the same periodicity as those generated at said first station.

4. A. transmission line inter :o'nnecting two stat ons, signaling apparatus at one: station a u a comprising a vibrating relay controlled by v low frequency signaling current from said station, an oscillating circuit controlled by said relay and'tuned to -a frequency within the voice.range whereby there will be generated trains of oscillations flot' a periodicity controlled by the frequency of vibration vof said relay, and means for-coupling sa dcireuit to said line, and signaling apparatus at the other'stat'ion comprising relay nieans'ex clusively responsive to trainsof oscillations of the same periodicity as those generated at the first station, a norii'ially closed circuit controlled by said relay means, said normally" closed circuit including electrically retarding means and a relay, and a signal 40 controlling circuit controlled by said last: inentioned'rclay. A transmission-lme interconnecting-two stations, signal apparatusat each ofsaid stations comprising sending and receiving apparatus, said sending apparatus comprising a vibrating relay controlled by low -requeneysignaling current from thc station,

an oscillating circuit controlled by said relay tioncom )risingavi'b'fa'ting relay coiitrolled by low requency signaling current from said station, an oscillating circuit controlled by said relay and tuned to a frequency within the voice range whereb there will be generated trains of oscillations of a periodicity controlled by the frequency of vibration of said relay, and means for coupling said circuit to said line, and signaling ap-' paratus-at the other station comprising a vacuum tube detector, a transformer in the output of said tube tuned to be eilicient at the frequency of the aforementioned periodicity of said trains of oscillations, relay means in the output circuit of said tube exclusively responsive to trains of oscillations of the same periodicity as those generated at the first station, a normally closed circuit controlled by said relay means, said normally closed circuit including electrically retarding means and arelay, and a signal controlling circuit controlled by said last mentioned relay.

7. A transmission line comprising two line sections, each of said line sections being suitable for the transmission of signaling currents of diiferent frequencies, a composite ringer comprising means responsive to signal currents of one of said. frequencies and generating means controlled thereby for generating currents of the other of said requencies, and a single pair of conductors associated with said transmission line whereby the ;incoming currents of one of. said frequencies may beapplied to said responsive means and whereby the generated curapplied to said line.

t8. 'A transmission line interconnecting two stations means at one of said stations for generating current within the voice frequency range, means for; applying said current to said line in a periodically inteirupted manner according to a predetermined frequency, and signal receiving apparatus at the othersta'tion COIllpllSlll" means exclusively responsive to trains of oscillations of the same periodicity as those generated at the firststation, a normally closed circuit controlled by-said last'inentioned means,

'rentsfrom said generating means may be said normally closed circuit includingelcctrically retarding means, and a signal controlling circuit controlled by said last men 'tioned circuit.

9. A transmission line interconnecting two stations, means at one ofsaidstations forv generating current within the voice frequency range, means for applying said current to ,said line in a periodically interrupted manneraccording to a predetermined frequency; and receiving "means at said other station, said receiving means comprising arrangements tuned to be exclusively responsive to said signaling currents, a; signaljand electrical retarding arsaid tuned arrangements. v

10. A transmission line over which sigrangements vfor connectingsaid' signal to nailing 'rurrents are transmitted, said signaling currents'being of a. relatively high frequency and being interrupted in a periodic manner m-cnrding tu at predetermined relatively low frequency, and -recei\"ing means associated with said line. said receiving meanscmnprismg a (H'Clllt tuned to be exviusiveiy responsive to said signaling currents. a slow operating relay controlled by said circuit, and signaling means controlled 19 by said relay.

In testimony whereof we have signed our names to this specification this 16th 'day of November 1921. v

ALVA B. ennui. i

. DANFORTH K. GANNETT.

HARRY NYQUIST. 

